Transparent substrate provided with a silicon derivative layer

ABSTRACT

The subject of the invention is a transparent substrate, especially made of glass, provided on at least one of its faces with a layer based on an at least partially oxidized silicon derivative chosen from silicon dioxide or silicon oxides which are substoichiometric in terms of oxygen, silicon oxycarbide or silicon oxynitride, and having a hydrophilic character.

The invention relates to the deposition of thin layers, especially thosehaving an interferential thickness, on transparent substrates so as toconfer a particular functionality on them.

The transparent substrates may be made of an organic polymer, of a glassceramic or, preferably, of a glass, in various applications, detailedbelow, of the glazing, screen or mirror type.

A recurrent problem with transparent substrates of the glass type (orwith semi-transparent substrates) is that of they gradually becomefouled, requiring tedious periodic cleaning. Another problem is thephenomenon of condensation, when it causes undesirable misting incontact with water vapour and, beyond simple misting, a build-up ofwater droplets preventing vision.

At least partial solutions have already been proposed: thus, coatingsare known which are based on a fluoropolymer whose highly hydrophobicsurface allows water to be rejected and less dirt to be attached.Coatings having photocatalytic properties are also known, for examplethose comprising anatase-crystallized titanium oxide, which areeffective for degrading at least organic dirt by oxidation.

These various types of coating are effective but relatively complex.Furthermore, none of them solves all the above mentioned problemsoptimally. Thus, hydrophobic coatings do not prevent the condensationphenomenon and, in contrast, photocatalytic coatings are only trulyeffective when exposed to ultraviolet radiation and can therefore beused more outside a dwelling than inside it.

The invention therefore aims to find coatings which are simple to useand are capable of facilitating the cleaning of glass-type or similarsubstrates and/or of lessening the phenomenon of water vapourcondensation on their surface or at the very least of preventing thecondensation from resulting in the appearance of misting or of amultitude of droplets.

The subject of the invention is a transparent substrate, especially madeof glass, provided on at least one of its faces with a layer based on anat least partially oxidized silicon derivative chosen from silicondioxide, silicon oxycarbide or silicon oxynitride, and having ahydrophilic character.

Within the context of the invention, the silicon derivative may compriseonly the elements Si and O in the case of SiO₂, the elements Si, O and Nin the case of an oxynitride and the elements Si, O and C in the case ofan oxycarbide. However, the silicon derivative according to theinvention also includes materials furthermore containing, in minoramounts (by weight) compared with silicon, at least one metal such asaluminium, zinc or zirconium. The addition of a metal may have threeadvantages. By reactive sputtering, this addition amounts to “doping”the Si target in order to make it more conducting, thereby speedingup/facilitating the deposition. Furthermore, whatever the method ofdeposition (for example by pyrolysis), the addition of a metal of thealuminium type can increase the durability of the material, mostparticularly if it contains little or no carbon/nitrogen. Finally, theaddition of a controlled amount of this type of metal into the layermakes it possible to vary its refractive index, especially to increaseit (aluminium oxide has in an index of about 1.65, while zinc andzirconium oxides have an index of about 2).

Within the context of the invention, the silicon derivative alsoincludes silicon oxides which are substoichiometric in terms of oxygen,of formula SiO_(x), where x is less than 2.

The invention has thus revealed a novel characteristic of this type ofmaterial, namely a certain hydrophilicity giving it unexpectedproperties: it was noticed that the substrate, preferably glass,provided with this type of layer cleans much more easily than a bareglass (less friction force for cleaning the glass with a cloth, most ofthe dirt being removed without any effort by spraying water).Furthermore, the rate of fouling was observed to be less, making itpossible to reduce the frequency of the cleaning operations, this effectbeing more marked if the glass is on the outside and exposedperiodically to rain: by running down the glass, rain naturally carriesaway the dirt. The third unexpected effect is that any watercondensation phenomenon on the surface of the glass coated in this waydoes not reduce visibility through the glazing or reduces it verylittle: it seems that the water appears in the form of an invisible,transparent and homogeneous liquid film, and no longer in the form ofdroplets.

The same improvements are observed when comparing a glass provided witha multilayer film surmounted by the layer according to the inventionwith a glass provided only with the multilayer film (for example a filmhaving a solar-control or low-emissivity function or an opticalfunction, terminating in a layer which is chemically different from thatof the invention, for example a layer of a metal oxide or metalnitride).

These advantageous effects may be adjusted/increased by varying thechemical composition, the surface appearance and the method ofdeposition chosen.

Thus, the layer may have a refractive index of about 1.45 (pure SiO₂) orgreater than 1.45 in the case of a silicon suboxide or if the derivativecontains carbon or nitrogen. Advantageously, in the latter cases, therefractive index is adjusted to be between 1.45 and 1.80, especiallybetween 1.50 and 1.75 or between 1.55 and 1.68. The term “refractiveindex” should be understood to mean within the context of the inventioneither its refractive index within the usual meaning of the term whenthe layer is homogeneous with regard to composition and with regard toindex through its thickness, or its apparent average index when thelayer has a composition or an index which varies through its thickness.One advantageous embodiment of the invention relates in fact to layerswhose refractive index decreases from the carrier substrate to theexternal surface of the layer.

There are two advantages in choosing a low refractive index:

on the one hand, the index is close to that of the glass when this isthe substrate, thus preventing the glass from having a reflectiveappearance;

on the other hand, the more the refractive index tends to higher values,and the more the C or N content increases to the detriment of oxygen,and it turns out that the hydrophilicity of the layer is enhanced byincreasing its oxygen content.

Another parameter that can influence the hydrophilicity of the layer isits surface roughness which, in certain embodiments of invention, ismuch higher than that of a standard bare glass.

The layer according to the invention may be deposited by any type ofprocess capable of depositing thin layers of this type: the process maybe a vacuum process such as sputtering, especiallymagnetic-field-enhanced sputtering (for example starting with a silicontarget, optionally doped with boron or with aluminium). In order tofavour the formation on the surface of Si—OH groups favourable to highhydrophilicity, it is possible to use a reactive atmosphere containing,for example, in addition to a purely oxidising compound of the O₂ type,a compound containing hydrogen and/or to use a compound containing bothhydrogen and oxygen. The reactive atmosphere may thus contain an O₂/H₂,O₂/H₂O or H₂O₂ mixture when a silicon oxide is manufactured. When asilicon oxynitride is to be deposited, it is possible to use reactiveatmospheres comprising, as nitrogen and/or hydrogen compounds forexample, an amine, an imine, hydrazine or ammonia. The SiO₂ (optionallydoped with a small amount of a metal or with boron)—based layersdeposited by reactive sputtering may have quite variable refractiveindices. Depending on the deposition parameters chosen, especially thepressure when sputtering the target, the refractive index (averagedbetween 380 and 780 nm) of the layers may thus be in the region of1.4-1.5, resulting in quite dense layers. It may also have a lower valueof about 1.25-1.40, especially 1.28-1.35, for example, around 1.30 (towithin ±0.05). In this case, the layers are therefore less dense, with acertain amount of porosity and/or surface roughness which may favourtheir hydrophilicity.

Preferably, the deposition may be carried out by a sol-gel route or bypyrolysis, especially by CVD (Chemical Vapour Deposition). In the caseof deposition by a sol-gel route, the sol may comprise a precursor basedon tetraethyl orthosilicate TEOS and be deposited by known techniquessuch as dipping, spray coating or spin coating, or else the depositionmethod referred to as flow coating. In the case of deposition by CVD, asilicon precursor in the form of an SiH₄ type silane may thus be used.The silicon precursor may also be an organosilane, of the RSiX₃ type,where X is a halogen of the chlorine type and R is an alkyl (which islinear or branched, having, for example, from 1 to 10 carbon atoms ormore). It may be an organosilane of the R_(y)SiX_(4-y) type, with thesame conventions regarding R and X, or a compound belonging to thefamily of ethoxysilanes. Other gases/precursors may be added to thesilicon precursor(s), such as ethylene or a nitrogen-containingderivative such as ammonia or an amine (especially a primary amine). Anoxidising agent (O₂, H₂O, H₂O₂, etc, )may also possibly be present.

It has also been noticed that a certain amount of surface roughness inthe layer favours the above mentioned beneficial effects thereof, whichroughness can be controlled especially by the parameters governing thedeposition of the layer and by the actual preparation of the surface onwhich the layer proper is deposited.

The measured contact angle between water and the coatings according tothe invention is advantageously less than 35°, or less than or equal to25°, for example between 15° and 25°: this actually denoteshydrophilicity (to be compared with the contact angle on standard bareglass which is in general 40°). This is not necessarily a very highdegree of hydrophilicity which results in the beneficial effects of theinvention, or is even modest hydrophilicity, but, being significantlygreater than that of bare glass, it is effective. The condensationphenomenon is not necessarily eliminated, but it does prevent theappearance of drops (in fact when the contact angle is less than 7° or10°, the mist becomes invisible, even though condensation is stillpresent).

According to certain embodiments, and especially in the case of layersdeposited by CVD, the contact angle may be less than 15°, and evenespecially less than 10°.

The layer according to the invention may have a chemical compositionwhich varies through its thickness. Advantageously it may have an oxygenconcentration increasing towards its “external” surface (that is to sayits surface furthest away from the carrier substrate). It is thuspossible to have a silicon oxycarbide or oxynitride layer which ismarkedly richer in C or N near its surface closest to the substrate, andricher in O near its external surface, as far as even forming an almostpure (thin) layer of SiO₂ on top of a layer having a chemicalcomposition richer in C or in N; or even a layer of almost pure Si orSi₃N₄. This oxygen concentration gradient may be obtained by adjustingthe deposition conditions or by surface oxidation after deposition, forexample by a heat treatment.

A high oxygen concentration on the surface of the layer is in factfavourable in the sense that it results in a high content of hydroxylbonds Si—O—H on the surface, making it hydrophilic.

The layer according to the invention preferably has a thickness of atleast 5 nm, especially between 5 and 100 nm, for example between 10 and60 nm.

The layer of the invention may form part of a film of thin layers, bybeing the final layer of the film (or an additional layer to a givenfilm), this layer being the furthest from the substrate. It may, forexample, be an antireflection film (an alternation of layers with a highrefractive index and layers with a low refractive index, such asTiO₂/SiO₂/TiO₂/layer according to the invention, the TiO₂ possibly beingsubstituted with Nb₂O₅, Si₃N₄, SnO₂, etc). It may also be a film of thesolar-control type, such as a film of the type consisting of an optionalsublayer/TiN/layer according to the invention or a solar-control layerbased on TiO₂ or a mixed iron cobalt and chromium oxide: glazing thuscoated is sold by Saint-Gobain Glass France under the name“Vision-Lite”, “Starélio and “Antélio” respectively. It may also includemultilayer films comprising at least one silver-based layer having alow-emissivity or solar-control function (glazing thus coated being soldby Saint-Gobain Glass France under the name “Planitherm”), orlow-emissivity films whose functional layer is based on fluorine-dopedtin oxide (glazing thus coated being sold by Saint-Gobain Glass Franceunder the name of “EKO” glazing), or else solar-control films whosefunctional layer is based on steel or an Ni/Cr alloy (glazing thuscoated being sold by Saint-Gobain Vitrage under the name of “Cool-Lite”glazing). For further details, the reader may refer to the patentsEP-638 528, EP-718 250, EP-511 901, EP-728 712, W097/43224, EP-638 527and EP-573 325.

When the substrate is made of glass, it may be curved and/or toughenedor annealed before or after deposition of the layer or layers.

The subject of the invention is also the application of the substratesdescribed above to the manufacture of glazing with an “anticondensation”effect and/or an “antisoiling” effect and/or easily cleanable glazing(within the context of the invention, “anticondensation” means thatthere may be condensation, but it entails none or few of the negativeconsequences on visibility through the glazing). The glazing may be forbuildings, for vehicles, for mirrors, and most especially for bathroommirrors, rear view mirrors, shower cabinet glass, glazed doors andinternal partitions, urban furniture, display panels and display screensof the television or computer screen type.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with the help ofnon-limiting examples and the following figures:

FIGS. 1-3: photographs obtained by electron scanning microscopy (SEM) ofthe surface of a layer according to one of the examples.

In all the examples, 50 nm silicon oxycarbide layers were deposited on aclear silica-soda-lime glass of the “Planilux” type sold by Saint-GobainGlass France by CVD (for example, according to patent EP-518 755) usingSiH₄, ethylene and possibly an oxidising compound, by varying the amountof precursors and the deposition temperatures so that the layers hadrefractive indices of about 1.58 to 1.75. It was confirmed that it wasthe glasses coated with SiOC layers having the lowest refractive indiceswhich were the most hydrophilic and the most effective in terms ofreducing the rate of fouling. It was also these glasses that had themost pronounced “anticondensation” effect, although they had a contactangle with water which is not very low, about 15°-30°. It should benoted that the layers having a lower index tending towards that of theglass (index 1.52), therefore only modify the appearance of the glassvery little: other examples according to the invention have contactangles below 15° or 10°.

Coatings deposited by pyrolysis have the advantage of being able to becontinuously deposited directly in a float line.

The coatings as obtained are in general remarkably durable.

EXAMPLES 1-4

Table 1 below gives, for Examples 1, 2, 3 and 4, the refractive indicesn of four silicon-oxycarbide-based layers thus obtained, and the values(θ) of the contact angle with water after cleaning, and the result of atest consisting in storing the glasses coated with the layer foreighteen hours at 30° C. in an atmosphere having a relative humidity of95% (“YES” means that there is an “antimisting” effect, in the sensethat no visible water droplets appear on the layer, while “No” meansthat such droplets are visible to the naked eye). The cleaning, using asurfactant, was carried out in two steps, by rinsing with town water,the cleaning being completed by a final rinse using deionized water, andthen dried in a stream of nitrogen.

TABLE 1 n TEST Example 1 1.58 14° YES Example 2 1.68 23° YES Example 31.71 27° YES/NO Example 4 1.75 31° NO

From this data, it may be seen that the most beneficial layers are thosewhich have the lowest refractive index, less than 1.70. It is thesewhich also are the most hydrophilic and the richest in oxygen.

EXAMPLES 5-7

These consisted of a Planilux glass surmounted by a 50 nm layer of SiOCobtained as previously. Table 2 below gives, for these examples, theirrefractive indices n (the glasses were cleaned before deposition of thelayers, as previously).

TABLE 2 n Example 5 1.68 Example 6 1.58 Example 7 1.71

FIGS. 1-3 are photographs obtained by SEM of the layer according toExample 5, with three different magnifications. It may be noted thatthere is a particular surface porosity, with kinds of small blistersquite irregular in size and with quite flat tops. FIG. 3, taken at thehighest magnification, shows “blisters” whose base, in its largestdimension, is within the range 60-80 to 100-110 nm.

They are compared with a comparative example, Comparative Example 8,consisting of Planilux glass without a layer:

according to a laboratory test (“lab test”), in which they were storedfor one, six and fourteen days in the atmosphere described within thecontext of Examples 1-4, namely 30+ C. and 95% relative humidity;

according to an outdoor exposure test on an industrial site (“industrialsite test”), in which they were stored for one and ten days in anatmosphere at 30° C. and at 95% relative humidity.

The results (expressed as “YES” or “NO”, as in Table 1) are given inTables 3 and 4 below

TABLE 3 LABORATORY TEST 1 day 6 days 14 days Example 5 YES YES YES Comp.Example 8 YES NO NO

TABLE 4 INDUSTRIAL SITE TEST 1 day 10 days Example 6 YES YES Example 7YES YES Comp. Example 8 YES NO

These results show that the layers according to the invention have alasting “antimisting” effect, whereas the bare glass has this effectonly very temporarily.

Another test was carried out on Examples 6, 7 and Comparative Example 8:the haze of the glasses provided with the layers according to Examples 6and 7 and of the bare glass of Comparative Example 8 was measured after10 days' storage outdoors on an industrial site (the haze is the diffuselight transmission, expressed as a percentage in the known manner).

The results are as follows: Examples 6 and 7 after 10 days have alimited haze (which is less than 1%), whereas Comparative Example 8after 10 days had a significant haze (at least 5%) due to the build-upof dirt on the glass. This test confirms the fouling retardation effectof the layers according to the invention.

EXAMPLE 9

This example relates to a solar-control glass sold under the name“Antélio clair” by Saint-Gobain Glass France.

This is a 6 mm thick Planilux surmounted by a mixed Fe, Co, Cr oxidelayer approximately 45 nm thick deposited by liquid-phase pyrolysis in aknown manner.

According to the invention, a thin SiO₂-based layer according to theinvention was deposited on the mixed oxide layer by the sol-gel route.

The sol was made from a solvent, namely 2-propanol, from 0.3N HCl in H₂Oand from tetraethyl orthosilocate TEOS.

The layer was deposited and cured in a conventional manner. The layerobtained had a thickness of less than or equal to 20 nm and a refractiveindex of about 1.45.

Contact angle measurements were carried out via those being comparedwith a Comparative Example 10 consisting just of the glass/Fe, Co, Crmixed oxide Antélio glazing.

The following treatments were carried out in succession on ComparativeExamples 9 and 10:

(a)—cleaning as previously, ozone treatment and UV treatment in order toremove the carbon-containing species adsorbed on the surface of thelayer;

(b)—two days' ageing outdoors;

(c)—19 days' ageing outdoors;

(d)—cleaning test as previously

The contact angles with water were measured after each of these steps.The results are given in Table 5 below;

TABLE 5 EXAMPLE 9 COMPARATIVE EXAMPLE 10 (a) 17°  5° (b) 32° 53.1° (c)43° 79.3° (d) 24° 71°

It may be noted, from this data, that for Comparative Example 10, thecontact angle rapidly increases outdoors and that a standard cleaningoperation does not succeed in restoring a low contact angle. On theother hand, Example 9 becomes dirty much less quickly and its contactangle with water remains relatively low, even after several weeks; aboveall, the dirt comes off much more quickly after a standard cleaningoperation: the glazing easily becomes clean again

EXAMPLE 11

This example relates to the deposition of a layer based only on siliconand oxygen (possibly containing other elements, but only as impuritiesin negligible amounts). The layer was deposited on a “Planilux” glass,as in the case of Examples 1-4, by CVD using SiH₄ and an oxidisingcompound, but without ethylene. A 50 nm silicon oxide layer with anindex of 1.50 was obtained. Its contact angle with water, measured as inthe case of Examples 1-4, was low, less than 10° (about 7°). The layerhad the same antimisting effect as the layers of Examples 1 and 2.

What is claimed is:
 1. A transparent substrate having at least onesurface with a layer comprising at least one partially oxidized siliconderivative selected from the group consisting of silicon dioxide that issubstoichiometric in terms of oxygen, silicon dioxide, siliconoxycarbide and silicon oxynitride, wherein the substrate has ahydrophilic character and wherein the concentration of said partiallyoxidized silicon derivative is homogenous across the thickness of thelayer.
 2. The substrate according to claim 1, wherein the refractiveindex of the silicon-derivative layer is between 1.45 and 1.80.
 3. Thesubstrate according to claim 1, wherein the layer is deposited bysol-gel or by pyrolysis.
 4. The substrate according to claim 1, whereinthe layer is rough on the external surface.
 5. The substrate accordingto claim 1, wherein the contact angle between the surface of the layerand water is less than 35°.
 6. The substrate according to claim 1,wherein the layer has an oxygen concentration increasing towards itsexternal surface.
 7. The substrate according to claim 1, wherein thelayer has a high content of hydroxyl bonds Si—OH on the externalsurface.
 8. The substrate according to claim 1, wherein the layer has athickness of at least 5 nm.
 9. The substrate according to claim 1,wherein the layer is the last layer of a film of thin layers.
 10. Thesubstrate according to claim 1, wherein the substrate is curved,toughened, annealed or a combination thereof, before or after depositionof the layer.
 11. The substrate according to claim 1, wherein thesilicon derivative comprises at least one additive in a minor amountwith respect to silicon.
 12. The substrate of claim 1, wherein thesubstrate comprises glass.
 13. The substrate of claim 1, wherein therefractive index of the silicon-derivative layer is between 1.50 and1.75.
 14. The substrate according to claim 1, wherein the refractiveindex of the silicon-derivative layer is between 1.55 and 1.68.
 15. Thesubstrate according to claim 1, wherein the layer is deposited bychemical vapor deposition.
 16. The substrate according to claim 1,wherein the contact angle between the surface of the layer and water isless than or equal to 30°.
 17. The substrate according to claim 1,wherein the contact angle between the surface of the layer and water isbetween 15° and 25°.
 18. The substrate according to claim 1, wherein thecontact angle between the surface of the layer and water is less than orequal to 10°.
 19. The substrate according to claim 1, wherein the layerhas a thickness of between 10 nm and 60 nm.
 20. The substrate accordingto claim 9, wherein the film is an antireflection film, solar-controlfilm or a low emissivity film.
 21. The substrate according to claim 11,wherein the additive is a metal.
 22. The substrate according to claim21, wherein the metal is aluminum, zinc or zirconium.
 23. A glazingcomprising the substrate of claim
 1. 24. The glazing of claim 22,wherein the glazing is selected from the group consisting of a buildingglazing, a vehicle glazing, a mirror, a glazed door, an internalpartition, urban furniture, display panels, bathroom mirrors, rear-viewmirrors, display panels and display screens.
 25. A transparent substratehaving at least one surface with a layer comprising at least onepartially oxidized silicon derivative wherein the layer has an oxygenconcentration that increases across the layer in a direction towards theexternal surface wherein the surface closest to the substrate is almostpure silicon dioxide and wherein the partially oxidized siliconderivative is selected from the group consisting of silicon dioxide thatis substoichiometric in terms of oxygen, silicon dioxide, siliconoxycarbide and silicon oxynitride, wherein the substrate has ahydrophilic character.
 26. The substrate according to claim 25, whereinthe refractive index of the silicon-derivative layer is between 1.45 and1.80.
 27. The substrate according to claim 25, wherein the layer isdeposited by sol-gel or by pyrolysis.
 28. The substrate according toclaim 25, wherein the layer is rough on the external surface.
 29. Thesubstrate according to claim 25, wherein the contact angle between thesurface of the layer and water is less than 35°.
 30. The substrateaccording to claim 25, wherein the layer has an oxygen concentrationincreasing towards its external surface.
 31. The substrate according toclaim 25, wherein the layer has a high content of hydroxyl bonds Si—OHon the external surface.
 32. The substrate according to claim 25,wherein the layer has a thickness of at least 5 nm.
 33. The substrateaccording to claim 25, wherein the layer is the last layer of a film ofthin layers.
 34. The substrate according to claim 25, wherein thesubstrate is curved, toughened, annealed or a combination thereof,before or after deposition of the layer.
 35. The substrate according toclaim 25, wherein the silicon derivative comprises at least one additivein a minor amount with respect to silicon.
 36. The substrate of claim25, wherein the substrate comprises glass.
 37. The substrate of claim25, wherein the refractive index of the silicon-derivative layer isbetween 1.50 and 1.75.
 38. The substrate according to claim 25, whereinthe refractive index of the silicon-derivative layer is between 1.55 and1.68.
 39. The substrate according to claim 25, wherein the layer isdeposited by chemical vapor deposition.
 40. The substrate according toclaim 25, wherein the contact angle between the surface of the layer andwater is less than or equal to 30°.
 41. The substrate according to claim25, wherein the contact angle between the surface of the layer and wateris between 15° and 25°.
 42. The substrate according to claim 25, whereinthe contact angle between the surface of the layer and water is lessthan or equal to 10°.
 43. The substrate according to claim 25, whereinthe layer has a thickness of between 10 nm and 60 nm.
 44. The substrateaccording to claim 33, wherein the film is an antireflection film,solar-control film or a low emissivity film.
 45. The substrate accordingto claim 33, wherein the additive is a metal.
 46. The substrateaccording to claim 45, wherein the metal is aluminum, zinc or zirconium.47. A glazing comprising the substrate of claim
 25. 48. The glazing ofclaim 46, wherein the glazing is selected from the group consisting of abuilding glazing, a vehicle glazing, a mirror, a glazed door, aninternal partition, urban furniture, display panels, bathroom mirrors,rear-view mirrors, display panels and display screens.